Positive Temperature Coefficient Materials Research Articles

High temperature co-polyester thermoplastic elastomer nanocomposites for flexible self-regulating heating devices

Pyroresistive polymer composites are smart materials with great promise in numerous fields of electronic devices, including temperature and strain sensors, self-regulating heating, and over-current/over-temperature protective devices. However, the operational window of these materials is limited by the phase transition temperatures of the polymer matrix and the brittleness of the composites. Herein, a conductive polymer composite based on a co-polyester thermoplastic elastomer reinforced with graphene nanoplatelets (GNPs) was developed, which exhibits a positive temperature coefficient (PTC) switching temperature of 200 °C. This system shows a more gradual increase in resistivity with temperature and a less pronounced drop in resistivity past the critical transition temperature than other PTC composites. Moreover, Joule heating experiments revealed the ability to regulate at a predefined maximum temperature (within 150 – 200 °C), tuneable through parameters such as filler concentration, applied voltage and thermal boundary conditions, as also demonstrated by multiphysics simulations. Due to the more gradual PTC curve, this composite can produce steady state heating far below the PTC peak, unlike almost all other PTC materials: a unique advantage for self-regulating heating devices as the polymer is not in a melt state, reducing polymer degradation, filler mobility and increasing safety margin before onset of NTC behaviour.

Positive temperature coefficient material based on silicone rubber/ paraffin/ graphite/ carbon nanotubes for wearable thermal management devices

PTC materials provide substantial advantages such as adaptive temperature control performance and excellent safety. However, their use in wearable devices has been limited due to the essential requirements for flexibility and stability. This study prepared a new type of flexible PTC material, with a PTC intensity of 6.3 and a resistivity of only 400 Ω·cm in the low-temperature region. The flexibility of the material is evidenced by its 2 mm bending diameter and its ability to maintain structural integrity even after 100 bends. Furthermore, experimental evidence proves that PTC material has excellent thermal stability and can withstand extreme temperatures ranging from −20 °C to 120 °C. In the thermal control experiment, the PTC material maintains a temperature of approximately 25 °C to accommodate the requirements of the human body in a cold environment. When compared to the conventional PI heating sheet, the newly prepared PTC material exhibits advantages such as rapid response, adaptive temperature control performance, and safety. Consequently, it presents a broad application prospect in the field of wearable heating devices.

Performance Research on Heating Performance of Battery Thermal Management Coupled with the Vapor Injection Heat Pump Air Conditioning

Compared to the use of positive temperature coefficient (PTC) materials that consume electrical energy for low-temperature heating, heat pump air conditioners can provide more energy-efficient heating performance by absorbing and utilizing heat from the outdoor air to heat the cab in order to improve the range of electric vehicles. In addition, in order to make the battery work under safe working conditions, this paper proposes battery thermal management coupled with vapor injection heat pump air conditioning. The system is modeled and analyzed through simulation, and the impact of the compressor speed and ambient temperature changes in the battery cooling performance of the system. The results show that under different compressor RPM (Revolution Per Minute) with an ambient temperature of 5 °C, the average temperature of the battery pack remains below 30 °C, and the majority of individual cell temperatures are maintained within the range of 20 to 35 °C. At a constant compressor RPM of 4000/min under varying ambient temperatures, the average temperature of the battery pack remains below 30 °C, with the majority of individual cell temperatures staying within the range of 20 to 35 °C. And the battery cooling performance still performs well. In the low temperature of −10 °C and −20 °C, the system can still maintain a relatively stable heating capacity compared with the 2009.1W, provided by the environment temperature of 5 °C at the same RPM.

Development and application of the low Curie point positive temperature coefficient (PTC) electrothermal anti-icing material

The application of the positive temperature coefficient (PTC) materials in electrothermal anti-icing offers not only uniform heating of the anti-icing area, but also adaptive temperature control of the material. This study focuses on the preparation of a low Curie point PTC material with a Curie temperature point of 1 °C, using the in-situ polymerization method. The PTC behaviors of the material were extensively investigated by adjusting the component ratios and the microstructures of the materials were analyzed in correlation with scanning electron microscopy (SEM) images. Subsequently, adaptive temperature control and stability experiments were conducted to evaluate the material's performance. Eventually, the material was adopted to electrothermal anti-icing experiment for wind turbine blades. The results demonstrate that when the mass fraction of acetylene black is 9 wt%, the mass ratio of n-tetradecane/hydroxyl-terminated polydimethylsiloxane (HTPDMS) is 1:1, and the mass ratio of polydimethylsiloxane (PDMS)/HTPDMS is 1:2, the low-temperature resistivity of the low Curie point PTC material reaches an impressive value of only 5.37 Ω cm, the PTC intensity can reach 2.99, and the thermal conductivity can reach 0.778 W/(m·K). Furthermore, the material exhibits robust adaptive temperature control capability, effectively maintaining the temperature below 3 °C under different operating voltages and ambient temperatures. Even after 100 cyclic experiments, the material demonstrates superior PTC behavior, excellent temperature control ability, and exceptional stability. Additionally, under different operating voltages, ambient temperatures and wind speeds, the low Curie point PTC material exhibits excellent adaptive adjustment capability and maintains uniform heating of the anti-icing surface. These findings provide valuable insights for in-depth exploration of the low Curie point PTC electrothermal anti-icing materials.

Study on the low Curie point positive temperature coefficient (PTC) material based on the conductive model

PTC material is a positive temperature coefficient heat-sensitive material, and when used as a heating element for electrothermal anti-icing, it exhibits adaptive temperature control. This paper aims to establish and experimentally verify a conductive model for the low Curie point PTC material based on the distribution and blending characteristics of HTPDMS, PDMS, n-tetradecane and acetylene black. Additionally, various mass proportions of the low Curie point PTC materials in the conductive region are prepared and analyzed to understand their PTC effects. Finally, the feasibility of employing the low Curie point PTC material for electrothermal anti-icing is verified through anti-icing experiment. The results demonstrate that the resistivity of the materials with different mass proportions in the seepage and conductive regions conforms to the conductive model proposed in this study. Specifically, when the mass proportion of n-tetradecane/HTPDMS is 1:1, and the mass proportion of PDMS/HTPDMS is 1:2, the low Curie point PTC material exhibits a Curie temperature of 1 °C, with a low-temperature resistivity of only 5.37 Ω cm and a PTC intensity of 2.99. Notably, after subjecting the material to 100 thermal cycle experiments, there is no significant change in the Curie temperature point. The low-temperature resistivity slightly increases, while the PTC intensity declines marginally, and no obvious negative temperature coefficient (NTC) effect is observed, confirming the material's excellent stability. The findings of this study contribute to the understanding of the low Curie point PTC anti-icing materials and lay a solid foundation for their future application in anti-icing systems for fans, airplanes, and various surfaces.

Enhancement of PTC effect of polymer/CB composite by intermolecular forces between nitrile groups on silica surface and polymer chain

The application of positive temperature coefficient (PTC) materials in sensing and intelligent heating has been widely studied. However, challenges such as poor stability and limited choices of base materials still exist. In this study, functionalized silica containing nitrile groups was synthesized through thiol-ene click reaction and incorporated into HDPE/CB composites to improve the PTC performance by forming non-covalent bonds through molecular interactions between the methyl and nitrile groups. The results showed that these non-covalent bonds were disrupted with increasing temperature, resulting in a 0.2 increase in PTC intensity and improved PTC stability in the composite materials. Furthermore, it was found that introduction of this nitrile-functionalized silica also induced PTC behavior around 140 °C in other polymers such as polystyrene and polycarbonate. This work is believed to provide new insights into understanding PTC behavior, expanding the choices of base materials for PTC materials, and enabling the preparation of high-performance PTC materials.

Achieving superior pyroresistive reproducibility at HDPE/PVDF composites with tailored conductive phase size

AbstractCommercial conductive polymer composites (CPCs) with positive temperature coefficient (PTC) behavior usually suffer from inherent poor reproducibility of pyroresistive property. Herein, a conductive carbon black (CB)/high density polyethylene (HDPE)/polyvinylidene fluoride (PVDF) composite with outstanding PTC reproducibility were prepared through introducing cellulose nanocrystals (CNCs) grafted with methyl methacrylate (CNC‐g‐PMMA). Following the minimum interfacial energy mechanism, the CNC‐g‐PMMA tends to locate in PVDF of binary polymer composites. A much finer morphology of conductive CB/HDPE phase is hence obtained owing to the increasement of PVDF/HDPE viscosity ratio by introducing CNC‐g‐PMMA. Undergoing multiple repeated temperature cycles, the room temperature resistance and PTC intensity of as‐prepared material keep almost unchanged, which demonstrates superior PTC reproducibility. The improving mechanism of PTC reproducibility has also been illustrated in detail. This research provides a facile and valid strategy to enhance the PTC reproducibility and will vastly expand the application of PTC composites in the field of intelligent temperature management.Highlights Assembling binary polymer‐based PTC materials with cocontinuous structure Nanocrystals enables conductive HDPE phase with finer morphology. The precise ranges of viscosity ratio ensure the co‐continuous morphology. Small conductive phase size enhances P reproducibility. Narrow spatial domain restricts the self‐aggregation of conductive fillers.

Fabrication and performance evaluation of the flexible positive temperature coefficient material for self‐regulating thermal control

AbstractIn this study, three kinds of newly flexible positive temperature coefficient (PTC) materials are fabricated by a simple preparation method. Due to introducing the hybrid filler of carbon nanotube and carbon black, these materials exhibit remarkable PTC effect including the PTC intensity of more than four‐orders magnitude and the resistivity‐temperature coefficient of 154%/°C. The Curie points of PTC materials are regulated to room‐temperature range by the low melting phase and influenced by melting onset temperatures of their solid–liquid phase change. With the help of transmission electron microscope, the micro‐capsule structure of the phase change regions is observed, and the hybrid conductive fillers randomly distribute in the blend matrix to construct three‐dimensional conductive network. Using the PTC materials as a heating element, the equilibrium temperature of the controlled device can be maintained around their Curie point without any control method. Moreover, the adaptive thermal control effect becomes more obvious with the increase of ambient temperature and initial heating power. Furthermore, the thermal control accuracy fluctuates within 0.15°C without any external control method, and is improved to round 0.08°C in combination with the switch control method. This study provides a new method for the thermal control of electronic devices in the requirement of lightweight and miniaturization at low temperature environment.

Flash sintering in metallic ceramics: finite element analysis of thermal runaway in tungsten carbide green bodies

Flash sintering is a powerful tool for the ultrarapid consolidation of green ceramic compacts, although its activation mechanisms in electrically conductive PTC (Positive Temperature Coefficient for resistivity) materials' is poorly understood. It was argued that a flash event could be initiated and sustained for a transitory period in certain PTC ceramics because of an initial negative dependence of the green material resistivity with temperature. The thermal runaway phenomenon and its activation conditions on binderless tungsten carbide (WC) green bodies are investigated in the present work by numerical simulations using finite element methods (FEM). The flash event is recreated and studied within the COMSOL Multiphysics software at the macroscale, i.e., considering the flash as an electrical power surge driven by an increasing sample's conductivity. During the flash, very high temperatures in the range of 1800–2000 °C can be reached in the WC green sample in a few seconds. The accurate numerical simulation of such event results in heating rates exceeding 1000 °C/s, a condition that theoretically brings a powder compact at temperatures high enough to accelerate and prioritize sintering densifying mechanisms over non-densifying ones. Therefore, the sample's regions where the maximum sintering temperature is reached more slowly because of thermal contacts with the electrodes remain highly porous at the end of the process.

High-Temperature Response Polylactic Acid Composites by Tuning Double-Percolated Structures.

Due to the properties of a positive temperature coefficient (PTC) effect and a negative temperature coefficient (NTC) effect, electrically conductive polymer composites (CPCs) have been widely used in polymer thermistors. A dual percolated conductive microstructure was prepared by introducing the polybutylene adipate terephthalate phase (PBAT) into graphene nanoplatelets (GNPs)-filled polylactic acid (PLA) composites, intending to develop a favorable and stable PTC material. To achieve this strategy, GNPs were selectively distributed in the PBAT phase by injection molding. In this study, we investigated the crystallization behavior, electrical conductivity, and temperature response of GNP-filled PLA/PBAT composites. The introduction of GNPs into PLA significantly increased PLA crystallization capacity, where the crystallization onset temperature (To) is raised from 116.7 °C to 134.7 °C, and the crystallization half-time (t1/2) decreases from 35.8 min to 27.3 min. The addition of 5 wt% PBAT increases the electrical conductivity of PLA/PBAT/GNPs composites by almost two orders of magnitude when compared to PLA/GNPs counterparts. The temperature of the heat treatment is also found to play a role in affecting the electrical conductivity of PLA-based composites. Increasing crystallinity is favorable for increasing electrical conductivity. PLA/PBAT/GNPs composites also show a significant positive temperature coefficient, which is reflected in the temperature-electrical resistance cycling tests.

Polymer positive temperature coefficient composites with room-temperature Curie point and superior flexibility for self-regulating heating devices

Polymer PTC (positive temperature coefficient) materials with low switching temperature point are important for many electronic devices since the electronic devices usually work under room temperature range (0–40 °C). The desired polymer PTC materials for the application in thermal control of flexible electronics should also include room-temperature switching temperature, low room-temperature resistivity, good mechanical flexibility and adaptive thermal control performances. This work designed two new types of PTC materials with room-temperature switching temperature and excellent mechanical properties. They are prepared by mixing the semi-crystalline polymer EVA with low melting temperature (Tm) with the amorphous polymer (PS or PVAc) with low glass transition temperature (Tg), while the low-cost graphite is selected as conductive filler. The PTC materials were obtained with low switching temperature point (<30 °C) and low room temperature resistivity (102 Ω m), high PTC repeatability and flexibility, short heating response time and good adaptive thermal control performances.

Study on adaptive infrared camouflage of novel positive temperature coefficient (PTC) materials in space

In order to protect important military targets from the threat of advanced infrared detection systems and guided weapons, the development of adaptive infrared decoy technology has become a top priority. In this paper, the feasibility of applying PTC material to infrared camouflage of decoy was discussed for the first time. Meanwhile, a design method for performance parameters of PTC materials that satisfy the infrared camouflage was proposed with consideration given to the complex background environment in which the space decoy was located. Taking this as a guide, the room temperature PTC materials that attain the design requirements were prepared. In this paper, the phase change characteristics of the material and the change of thermal conductivity with temperature were considered, and the heat transfer model of the PTC material was further optimized, which was verified by experiments in a vacuum environment. On this basis, the infrared camouflage properties of space decoy based on thermal control of PTC materials were further simulated. The results show that the PTC resistor prepared under the guidance of this design method can achieve a more ideal infrared camouflage effect and higher adaptive temperature control precision than ordinary resistors when applied to space decoy. The research results specify possible directions for the development and thermal control of PTC material.

Positive temperature coefficient (PTC) materials based on amorphous poly(methyl methacrylate) with ultrahigh PTC intensity, tunable switching temperature and good reproducibility

Positive temperature coefficient (PTC) materials based on amorphous polymers usually suffer from low intensity owing to their relatively small volume thermal expansion. Herein, graphene nanoplatelets (GNPs) and carbon fibers (CF) with large aspect ratios were introduced into amorphous poly(methyl methacrylate) (PMMA) via melting mixing followed by hot pressing to improve the PTC characteristics of the conductive composites. The binary PMMA/GNPs composites showed good reproducibility while the PMMA/CF composites were superior in PTC intensity and their switching temperature (positive to negative temperature coefficient) could be tuned by varying the CF concentrations. When the both binary composites were connected in series, their strengths could be fostered and their weaknesses could be circumvented. The ternary composite exhibited a superior PTC intensity of 7.17, outperforming most of the reported PTC materials. These composites have great potential for applications as temperature sensors and current limiting devices.

Advances in Prevention of Thermal Runaway in Lithium‐Ion Batteries

The prevention of thermal runaway (TR) in lithium‐ion batteries is vital as the technology is pushed to its limit of power and energy delivery in applications such as electric vehicles. TR and the resulting fire and explosion have been responsible for several high‐profile accidents and product recalls over the past decade. Herein, the causes of TR are described and novel preventative methods are examined, approaching the problem from different angles by altering the internal structure of the battery to undergo thermal shutdown or developing the battery and thermal management systems so that they can detect and prevent TR. Ultimately, a variety of different technologies is needed to address the emerging market of highly specialized lithium‐ion batteries. Key innovations discussed include positive temperature coefficient (PTC) materials, self‐healing polymer electrolytes, and hybrid liquid–solid‐state electrolytes. Mist cooling achieves a highly uniform temperature inside the battery pack without the need for pumps to circulate a coolant. The development of battery management systems (BMSs) which model the internal temperature of the cell from real‐time data and prevent the cell reaching a critical temperature is an essential area for further research.

Facile and Effective Positive Temperature Coefficient (PTC) Layer for Safer Lithium-Ion Batteries

With the popularization of lithium-ion battery propelled electric vehicles, the safety requirements of lithium-ion batteries are under immense scrutiny. Minimizing catastrophic cell failure events by developing improved safety features for lithium-ion batteries is an important endeavor. Herein, we report a novel, safe cathode configuration, achieved by sandwiching a positive temperature coefficient (PTC) material layer between the Al foil and active cathode material. The PTC layer (2–3 μm thick) was a composite of the carbon-coated LiFePO4(C-LFP), poly(vinylidene fluoride) (PVDF), and Super P. Due to the structural stability, good conductivity, and limited amount of C-LFP, the PTC layer maintained good structural integrity as a supporting layer between the Al current collector and active material layer. At high temperatures (>80 °C), the PTC effect was triggered in the protective layer by PVDF volume expansion, which effectively disrupted electron flow, leading to a dramatic increase in cathode resistance, thus preventing thermal runaway from occurring. Such a PTC layer-containing cell design not only shows outstanding safety performance during overheating scenarios but also has no degradation on cell performance. Furthermore, the PTC layer has good processability and is a convenient and practical material layer for commercial applications.

Economical conductive graphite‐filled polymer composites via adjustable segregated structures: Construction, low percolation threshold, and positive temperature coefficient effect

AbstractThe economical graphite‐filled thermoplastic urethane/ultra‐high molecular weight polyethylene (TPU/UHMWPE) composites with the segregated structure were constructed by the combination of mechanical crushing and melt blending method. The low percolation threshold of 1.89 wt% graphite in the adjustable segregated composites was obtained and high electrical conductivity was about 10−1 S m−1 at 10 wt% graphite loadings owing to the formation of three‐dimensional conductive networks. Moreover, when the graphite loadings were over the percolation threshold, the remarkable positive temperature coefficient (PTC) effect of electrical resistivity for TPU/UHMWPE‐Graphite composites were achieved, originating from the combined thermal motion of TPU and UHMWPE. Meanwhile, the outstanding repeatability of PTC effects was obtained after 5‐time cycles. Therefore, economical conductive polymer composites were still the promising field in the practical application of PTC materials.

Black Phosphorus@Laser‐Engraved Graphene Heterostructure‐Based Temperature–Strain Hybridized Sensor for Electronic‐Skin Applications

AbstractSmart electronic skin (e‐skin) requires the easy incorporation of multifunctional sensors capable of mimicking skin‐like perception in response to external stimuli. However, efficient and reliable measurement of multiple parameters in a single functional device is limited by the sensor layout and choice of functional materials. The outstanding electrical properties of black phosphorus and laser‐engraved graphene (BP@LEG) demonstrates a new paradigm for a highly sensitive dual‐modal temperature and strain sensor platform to modulate e‐skin sensing functionality. Moreover, the unique hybridized sensor design enables efficient and accurate determination of each parameter without interfering with each other. The cationic polymer passivated BP@LEG composite material on polystyrene‐block‐poly(ethylene‐ran‐butylene)‐block‐polystyrene (SEBS) substrate outperforms as a positive temperature coefficient material, exhibiting a high thermal index of 8106 K (25–50 °C) with high strain sensitivity (i.e., gauge factor, GF) of up to 2765 (&gt;19.2%), ultralow strain resolution of 0.023%, and longer durability (&gt;18 400 cycles), satisfying the e‐skin requirements. Looking forward, this technique provides unique opportunities for broader applications, such as e‐skin, robotic appendages, and health monitoring technologies.

A dimensionless study on thermal control of positive temperature coefficient (PTC) materials

Positive temperature coefficient (PTC) material is widely used in the field of thermal control due to its unique temperature sensitive characteristics. However, there is no general criterion about PTC material thermal control at present due to the lack of theoretical analysis in the previous works. Thus, in this paper, the dimensionless method is used to study PTC material adaptive thermal control and finally, a fitting formula is obtained to estimate the equilibrium temperature of controlled device. First, a one-dimensional and steady-state heat transfer model was proposed to calculate the equilibrium temperature of controlled device under thermal control of PTC materials, and it was verified by experiment. Then, the model has been nondimensionalized and four dimensionless numbers are introduced by Buckingham theorem, in which the Wr number is presented to represent the heating characteristics of PTC materials. Finally, by fitting all the data, a form of fitting equation of equilibrium temperature of controlled device is obtained. The results show that this form proposed in this paper can be applied to the widely used ceramic PTC materials. The criterion equation fitted by this form can effectively estimate the equilibrium temperature of the controlled devices with good accuracy and wide application.

Designs of conductive polymer composites with exceptional reproducibility of positive temperature coefficient effect: A review

AbstractConductive polymer composites with positive temperature coefficient (PTC) effect have gained intensive attention for the potential application in the smart heating field. The PTC reproducibility is significantly essential to guarantee the security and utility of PTC composites. Regrettably, during the repeated temperature cycles, the irreversible self‐aggregation of conductive filler and the random reconstruction of conductive network lead to unsatisfactory performance of PTC reproducibility. Extensive efforts have been conducted to address this issue by strategies, including modification of fillers, cross‐linking of a polymer matrix, hybrids of fillers, and application of binary polymer matrix. Nevertheless, there are very limited reviews about this issue. In this review, the recent advances in fabricating PTC composites with the enhanced PTC reproducibility have been systematically summarized. Meanwhile, the current challenges and future prospects of PTC composite are also presented. We hope that this review will provide some inspirations for designing PTC materials of long‐term performance for commercial applications.

Improving Resistance‐Temperature Characteristic of Polyethylene/Carbon Black Composites by Poly(3,4‐Ethylenedioxythiophene)‐Functionalized Multilayer Graphene

AbstractPolymeric positive temperature coefficient (PTC) materials can be used to install “brake” technology for the thermal runaway of lithium‐ion batteries. However, it still has poor cycle stability and obvious negative temperature coefficient (NTC) effect, which reduces the reliability of the material. In order to solve these problems, conductive polymer poly(3,4‐ethylenedioxythiophene) (PEDOT) modified multilayer graphene (MLG) conductive additive (PEDOT‐MLG) is introduced into middle density polyethylene/carbon black (MDPE/CB) system. Compared with the conventional modification, the PEDOT modified MLG shows high conductivity and excellent thermal stability. In addition, the introduction of PEDOT‐MLG into MDPE/CB can further reduce the room temperature resistivity due to the good compatibility between the modified graphene and the matrix, thus improving the PTC intensity to 7.1. What is more, MLG limits the re‐aggregation of CB particles when the temperature further rises, which effectively weakens the NTC effect.